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Filtered beer refers to any
ale
Ale is a Type of beer, type of beer brewed using a Warm fermentation, warm fermentation method, resulting in a sweet, full-bodied and fruity taste. Historically, the term referred to a drink brewed without hops.
As with most beers, ale typicall ...
,
lager
Lager () is beer which has been brewed and conditioned at low temperature. Lagers can be pale, amber, or dark. Pale lager is the most widely consumed and commercially available style of beer. The term "lager" comes from the German for "storage" ...
, or
fermented malt beverage in which the sediment left over from the brewing process has been removed. Ancient techniques included the use of straw mats, cloth, or straws, and frequently left some sediment in the drink. Modern filtration, introduced at the end of the 19th century, uses a mechanical process that can remove all sediment, including yeast, from the
beer
Beer is one of the oldest and the most widely consumed type of alcoholic drink in the world, and the third most popular drink overall after water and tea. It is produced by the brewing and fermentation of starches, mainly derived from ce ...
. Such beer is known as
bright beer
Bright beer is beer in which yeast is no longer in suspension. There are several methods used for clearing yeast from beer, from waiting for the yeast to drop of its own accord ("dropping bright") to filtering it.
Dropping bright
When the conce ...
and requires
force carbonation
Carbonation is the chemical reaction of carbon dioxide to give carbonates, bicarbonates, and carbonic acid. In chemistry, the term is sometimes used in place of carboxylation, which refers to the formation of carboxylic acids.
In inorganic ch ...
before bottling or serving from a keg. In the
United Kingdom
The United Kingdom of Great Britain and Northern Ireland, commonly known as the United Kingdom (UK) or Britain, is a country in Europe, off the north-western coast of the continental mainland. It comprises England, Scotland, Wales and North ...
, a beer which has been filtered in the brewery is known as "brewery-conditioned", as opposed to unfiltered
cask ales.
Filtration
Beer is mechanically filtered by flowing the beer through layers of filter material; the two main techniques are surface filtration and cake filtration. Filters range from rough filters that remove much of the yeast and any solids (e.g. hops, grain particles) left in the beer, to filters fine enough to strain colour and body from the beer. The normal filtration ratings are defined as rough, fine or sterile. Rough filtration leaves some cloudiness in the beer, but it is noticeably clearer than unfiltered beer. Fine filtration yields a beer which is nearly transparent and not cloudy, although observation of the
scattering of light through the beer will reveal the presence of some small particles. Finally, as its name implies, sterile filtration is fine enough that almost all microorganisms in the beer have been removed. Beer which has been filtered is usually held in "bright tanks" at the brewery before bottling or additional treatment.
A beer which is filtered is stable, so all conditioning has stopped - as such it is termed "brewery-conditioned". Beers which are in contact with the yeast are known as
bottle-conditioned or
cask-conditioned.
Sheet filters use pre-made media and are relatively straightforward. The sheets are manufactured to allow only particles smaller than a given size through, and the brewer is free to choose how finely to filter the beer. The sheets are placed into the filtering frame, sterilized (with hot water, for example) and then used to filter the beer. The sheets can be flushed if the filter becomes blocked, and usually the sheets are disposable and are replaced between filtration sessions. Often the sheets contain powdered filtration media to aid in filtration.
Pre-made filters have two sides: one with loose holes, and the other with tight holes. Flow goes from the side with loose holes to the side with the tight holes, with the intent that large particles get stuck in the large holes while leaving enough room around the particles and filter medium for smaller particles to go through and get stuck in tighter holes.
Sheets are sold in nominal ratings, and typically 90% of particles larger than the nominal rating are caught by the sheet. For sterile filtration, a typical size is 1
micrometre
The micrometre ( international spelling as used by the International Bureau of Weights and Measures; SI symbol: μm) or micrometer (American spelling), also commonly known as a micron, is a unit of length in the International System of Unit ...
or less.
Filters that use a powder medium are considerably more complicated to operate, but can filter much more beer before needing to be regenerated. Common media include
diatomaceous earth
Diatomaceous earth (), diatomite (), or kieselgur/kieselguhr is a naturally occurring, soft, siliceous sedimentary rock that can be crumbled into a fine white to off-white powder. It has a particle size ranging from more than 3 μm to le ...
(kieselguhr) and
perlite
Perlite is an amorphous volcanic glass that has a relatively high water content, typically formed by the hydration of obsidian. It occurs naturally and has the unusual property of greatly expanding when heated sufficiently. It is an industrial m ...
.
Cold filtering
Though all filtering is done cold, the term ''cold filtering'' is used for a filtering process in which the beer is chilled so the protein molecules clump together and are easier to filter out. Breweries tend to differentiate cold filtered beers from those that have been heat pasteurised.
Garrett Oliver
Garrett Oliver (born July 29, 1962) is an American brewer and beer author from New York City. Since 1994, he has worked as the brewmaster at the Brooklyn Brewery.
Early life
Oliver grew up in Hollis, Queens to a father who enjoyed hunting and coo ...
, ''The Brewmaster's Table'', page 19.
Bright beer
When a beer has been left to allow the yeast to settle at the bottom of the vessel in which it is held (usually a conditioning or lagering tank), it has "dropped bright".
Finings
Finings are substances that are usually added at or near the completion of the processing of brewing wine, beer, and various nonalcoholic juice beverages. They are used to remove organic compounds, either to improve clarity or adjust flavor or ar ...
can be introduced during the production of beer in order to induce it to drop bright more readily.
Home brewed beer
Beer filtration is also common on a small scale. It is not uncommon for homebrewers (those who brew their own beer at home, often in small batches around ) to filter their own beer. While they lack the sophisticated equipment of large-scale breweries, they can achieve satisfactory results using canister filters with successive, replaceable filter cartridges or pads. Most homebrewers will only filter their beer down to 5
μm to remove the majority of yeast and sediment, although some may filter their beer down to 1.0 or 0.5 μm. Anything smaller introduces risk of removing flavor and beneficial compounds.
References
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Brewing
Beer vessels and serving